钙矾石法去除脱硫废水硫酸根沉淀物沉降特性研究

One of the main challenges in zero liquid discharge of industrial wastewater is ineffective removal of sulfate and the consequent scaling in concentration and evaporation units. Effects of initial n(Ca²⁺)/n(SO₄^2-)(ICS), initial n(Al³⁺)/n(SO₄^2-)(IAS)and mixing conditions on sulfate removal and precipitate settling by ettringite precipitation were investigated by using flue gas desulfurization wastewater. Composition and morphology of the precipitate were characterized by scanning electron microscope, X-ray diffraction, et al. The results showed that ettringite precipitation achieved sulfate removal as high as 99.5%, but harvested precipitate with higher Zeta potential and thus deteriorating settling performance. Changing of ICS and IAS altered structural, morphological and settling properties of the precipitates. Increasing ICS improved both sulfate removal and settleability of the precipitate. Increasing IAS made sulfate removal increased firstly and then decreased, but improved settleability of the precipitate. Dosing polyacrylamide could effectively improve the settling performance of the precipitate, and the 30 min sludge volume of precipitate could decrease to 30.5% after dosing cationic polyacrylamide with branched structure, high molecular weight and cation degree of 39%.